1. Field of the Invention
The present invention relates to an apparatus monitoring method and an apparatus monitoring system and relates to, for example, a technique for judging abnormality of an apparatus from values of a sensor.
2. Related Art
There is an increasing need for remote monitoring for improvement of safety of apparatuses and reduction in monitoring cost. There is monitoring of abnormality as one of matters that should be realized in the remote monitoring. Abnormality of an apparatus is judged from a value of a sensor. An upper limit and a lower limit of values that should be taken by the sensor are given. When a value of the sensor deviates from this range (a normal range), the apparatus is considered abnormal. It is possible to determine the upper limit and the lower limit of sensor values by using history data of sensor values. For example, there is a method of, assuming that fluctuation in sensor values is a normal distribution, calculating an average “μ” and a standard deviation “σ” and setting μ±3σ as an upper limit and a lower limit.
The remote monitoring has a characteristic that a large number of identical apparatuses are objects of monitoring. It is difficult to collect sensor data in all of these apparatuses and determine an upper limit and a lower limit. Since there is no history data of sensor values of an apparatus installed anew, it is impossible to set an upper limit and a lower limit. Therefore, a method of sampling several apparatuses among the object apparatuses and determining an upper limit and a lower limit using sensor data of the apparatuses sampled is conceivable. However, it is likely that there are individual differences among apparatuses even if the apparatuses are identical. It may be difficult to uniquely determine an upper limit and a lower limit of sensor values of the remaining apparatuses from the sensor data of the apparatuses sampled. In other words, an upper limit and a lower limit of sensor values determined from the apparatuses samples are not always satisfactorily adapted to finding of abnormality of the remaining apparatuses.